1. Field of the Invention
The present invention generally relates to vibration absorbers and, more specifically, to an active dual mass absorber for vibration control.
2. Description of the Related Art
Dynamic passive vibration absorbers have been successfully used in industry to attenuate structural vibration for both narrow and broad-band excitations. The invention is directed to a device which is used in an active control methodology for damping vibrations (e.g., engine sounds and vibrations in aircraft, vibrations on buildings, vibrations emanating from power plants, etc.).
More recently, the performance of these passive devices has been enhanced through the addition of an active component. Currently available dynamic vibration absorbers utilize a single reaction mass connected to the structure to be controlled, wherein the active force is applied between the reaction mass and the structure to be controlled.
The active component in a conventional vibration absorber consists of a self-balanced force generating member applied between the absorber mass and the structure to be controlled. The force generating member generally exerts an equal force in opposite directions and could include any common device, such as piezoelectric patches, electromagnetic devices, and so forth. Such a conventional structure is sometimes referred to herein as a single mass (single reaction mass) absorber.
Such conventional hybrid passive/active dynamic vibration absorbers provide improved response attenuation over that achieved by the passive system at the expense of the energy added to the system via the control force. The required control effort is a function of both the absorber mass and the frequency tuning (i.e. the ratio of the absorber's frequency to the structure's natural frequency).
A detuned absorber requires larger control forces than a tuned absorber. In some applications, these drawbacks limit the implementation of hybrid absorbers due to constraints in size, weight, and/or required control force magnitudes.
FIG. 1 is a schematic illustration of a conventional single active dynamic vibration absorber ("DVA") or reaction mass system. This system consists of a single reaction mass 10 attached to the structure to be controlled 11, 14, 15 through a spring 12 and damper 13 system. The structure to be controlled may be represented by a mass-spring-damper system 11, 14, 15.
In the system illustrated in FIG. 1, an active force is applied by a force generating member 16 between the reaction mass 10 and the structure to be controlled 11. A motion sensor 17 detects the motion of the structure 11 and relays this information to the force generating member 16 via a filter compensator 19 and line 18.
In operation, a disturbance force F(t) acts on the structure 11. Motion sensor 17 senses the motion of structure 11 and, by an operation known as "feedback", supplies the force generating member 16 with a signal via filter 19 and line 18. Force generating member 16 applies equal and opposite forces to the reaction mass 10 and the structure 11 to eliminate the movement of member 11.
A similar operation known as "feedforward" is substantially similar to the feedback operation, except that the line 18 is connected to element causing the disturbance force F(t) (not illustrated) and the filter 19 is adjusted. The signal from the motion sensor 17 changes the force F(t) to damp the movement of the structure 11.